Method for soldering work pieces

ABSTRACT

The invention describes a method of brazing workpieces ( 16 ) with a torch ( 10 ), in particular a plasma or welding torch, having an electrode ( 28 ), in which a transmitted and/or non-transmitted working arc supplied with power from a power source or a current source ( 2 ) is produced in order to generate a plasma beam from a delivered plasma gas, whereby at least one filler material ( 38 ) is fed to the seam region of the workpieces ( 16 ) to be joined. The filler material ( 38 ) is connected to the or to another power source or current source ( 39 ). To this end, one potential ( 40 ) of the power source or current source ( 39 ) is applied to the filler material ( 38 ) and the other potential ( 35, 41 ) to the workpieces ( 16 ). The power source or current source ( 39 ) is regulated in such a way that when the filler material ( 38 ) is lifted off the workpiece ( 16 ) an arc is prevented from being generated.

[0001] The invention relates to a method of brazing workpieces with atorch, in particular a plasma or welding torch, as well as a plasma orwelding torch of the type outlined in the introductory parts of claims 1and 11.

[0002] A method of brazing workpieces with a torch, in particular aplasma torch, with a non-consumable electrode is disclosed in patentspecification WO 98/21000 A1. Power is applied from a current source toan arc at the torch, which is transmitted or not transmitted, in orderto produce a plasma beam from a delivered plasma gas. A filler materialis delivered to the seam region of the workpieces to be joined, whichbecomes liquid due to the heat energy of the plasma beam or arc, causingthe filler material to form a pool of melt in the seam region of the twoworkpieces. The disadvantage of this is that a considerable amount ofheating energy must be generated by the plasma beam or arc in order toliquefy the filler material, which significantly reduces the temperatureof the melt pool.

[0003] The underlying objective of the invention is to propose a methodof brazing workpieces as well as a plasma or welding device, whereby theprocess stability for a brazing process is improved.

[0004] This objective is achieved by the invention due to the fact thatthe filler material is connected to the or to another power source orcurrent source and to this end one potential of the power source orcurrent source is applied to the filler material and the other potentialto the workpieces, and the power source or current source, in particularthe power delivered by the current source, is controlled in such a waythat when the filler material is lifted off the workpiece, an arc isprevented from being struck.

[0005] The advantage of this is that by supplying the filler materialwith power, in particular electrical energy, it can be heated separatelyirrespective of external influences, in particular heat generated by theplasma beam or working arc, to a temperature that is below the meltingpoint of the filler material, requiring only a very low amount of energyto be applied in order to transform the filler material into the liquidstate, in particular via the working arc or plasma beam generated. Thismeans that the heat applied via the torch, in other words the powersupply of the torch, can be very significantly reduced, therebypreventing the base material of the workpieces from melting. Anothermajor advantage is that by using the so-called hot wire technique, inother words by pre-heating the filler material, a very high melt pooltemperature can be obtained, which considerably improves the wettabilityof the liquid filler material, in particular the braze, simultaneouslyimproving the reliability of the process without having to introducemore energy into the base material of the workpieces. This is achieveddue to the fact that in order to render the filler material liquid, onlya very small amount of heat energy is drawn from the plasma beam orworking arc and almost the entire energy supplied by the plasma beam orworking arc is available for heating the base material of the workpiecesand the pool of melt. Another advantage is that pre-heating the fillermaterial improves the process of melting the filler material, therebypreventing spatter.

[0006] Other advantageous features are described in claims 2 to 10. Theresultant advantages may be found in the description.

[0007] The objective is also achieved by means of the features definedin the characterising part of claim 11. The advantage of this approachis that the filler material can be supplied with energy using only oneother current source or by using another current circuit which can becontrolled and regulated separately, achieving a significant improvementto the process stability.

[0008] Finally, an embodiment such as that defined in claim 12 is ofadvantage because the base material of the workpieces can be preventedfrom melting.

[0009] The invention is illustrated in detail on the basis of examplesof embodiments illustrated in the drawings.

[0010] The embodiments of the invention will be described in more detailbelow.

[0011] Of the drawings:

[0012]FIG. 1 is a schematic diagram of a welding machine or a weldingapparatus;

[0013]FIG. 2 is a simplified schematic diagram illustrating thestructure of a plasma torch and the components needed to implement themethod;

[0014]FIG. 3 is a simplified schematic diagram illustrating thestructure of a welding torch and the components needed to implement themethod.

[0015] Firstly, it should be pointed out that the same parts describedin the different embodiments are denoted by the same reference numbersand the same component names and the disclosures made throughout thedescription can be transposed in terms of meaning to same parts bearingthe same reference numbers or same component names. Furthermore, thepositions chosen for the purposes of the description, such as top,bottom, side, etc,. relate to the drawing specifically being describedand can be transposed in terms of meaning to a new position when anotherposition is being described. Individual features or combinations offeatures from the different embodiments illustrated and described may beconstrued as independent inventive solutions or solutions proposed bythe invention in their own right.

[0016]FIG. 1 illustrates a welding system and a welding device 1 andplasma apparatus for running a whole range of welding processes, e.g.MIG-MAG welding and WIG/TIG welding or electrode welding processes,double wire/tandem welding processes, plasma or brazing processes.Clearly, the solution proposed by the invention may be used with acurrent source or a welding current source.

[0017] The welding device 1 or the plasma device has a power source or acurrent source 2 with a power component 3, a control system 4 and aswitching element 5 co-operating with the power component 3 and controlsystem 4. The switching element 5 or the control system 4 is connectedto a control valve 6 incorporated in a supply line 7 for a gas 8, inparticular a protective gas such as C0 ₂, helium or argon and such like,running between a gas storage 9 and a torch or welding torch 10.

[0018] Furthermore, a wire feed device 11 such as commonly used forMIG-MAG welding may also be activated via the control system 4 in orderto feed an filler material or welding wire 13 from a supply reel 14through a supply line 12 into the region of the torch 10. Clearly, thewire feed device 11 could also be integrated in the welding device 1, inparticular in the basic housing, in a manner known from the prior art,rather than used as an add-on device as illustrated in FIG. 1.

[0019] It would also be possible for the wire feed device 11 to feed thewelding wire 13 or filler material to the process area externally to thetorch 10 or welding torch, in which case the torch 10 is preferablyprovided with a non-consumable electrode.

[0020] The current needed to strike an arc 15, in particular a workingarc, between the welding wire 13 or non-consumable electrode and aworkpiece 16 is fed via a supply line 17 from the power component 3 ofthe current source 2 to the welding torch 10, in particular to thewelding wire 13 or electrode, and the workpiece 16 to be welded is alsoconnected to the welding device 1, in particular to the current source2, via another supply line 18 so that a current circuit can beestablished across the arc 15 in order to run a process.

[0021] In order to cool the torch 10, the torch 10 can be connected viaa cooling circuit 19, with an integrated flow indicator 20, to a fluidcontainer, in particular a water container 21, so that the coolingcircuit 19, in particular a fluid pump used to pump the liquid containedin the water container 21, can be activated when the torch 10 isswitched on, thereby enabling the torch 10 and the welding wire 13 to becooled.

[0022] The welding device 1 also has an input and/or output device 22,by means of which a whole range of settings can be entered for weldingparameters and operating modes or welding programmes of the weldingdevice 1 or plasma device. The welding parameters, operating parametersor welding programmes entered at the input and/or output device 22 arethen forwarded to the control system 4, from where they are applied tothe individual components of the welding system and the welding device1.

[0023] In the embodiment illustrated as an example here, the torch 10 isalso connected to the welding device 1 and the welding system by meansof a hose pack 23. The individual lines from the welding device 1 to thetorch 10 are disposed in the hose pack 23. The hose pack 23 is connectedby means of a connector device 24, known from the prior art, to thetorch 10, whilst the individual lines in the hose pack 23 are connectedto the individual contacts of the welding device 1 by means ofconnecting sockets and plug connectors. To relieve tension on the hosepack 23, the hose pack 23 is connected via a tension-relieving device 25to a housing 26, in particular the basic housing of the welding device1.

[0024] It should basically be pointed out that not all the componentsmentioned above necessarily have to be used for the various weldingprocess and welding devices, such as WIG devices or MIG/MAG devices orplasma devices.

[0025]FIG. 2 is a very simplified, schematic diagram showing thestandard structure used for the torch, which is a commercially availableplasma torch.

[0026] For operating purposes, the torch 10 has a plasma nozzle 27, inwhich a non-consumable electrode 28 is disposed, whereby a plasma gas,delivered externally as schematically indicated by arrow 30, is fedthrough a passage 29 of the plasma nozzle 27. It is also possible forthe plasma nozzle 27 to be enclosed by a gas nozzle 31. This being thecase, another passage 32 will in turn be provided between the plasmanozzle 27 and the gas nozzle 31 and supplied externally with aprotective gas, as schematically indicated by arrow 33.

[0027] In terms of power supply, the torch 10 is connected to the powersource or the current source 2, to enable a working arc or arc 15, whichmay or may not be transmitted, to be built up in order to produce aplasma beam from the delivered plasma gas. In the embodiment illustratedas an example here, the power supply for the working arc or arc 15 isproduced by connecting the non-consumable electrode 28 to a potential34, in particular negative, of the current source 2. In order to able togenerate a transmitted working arc, the other, in particular thepositive potential 35 of the current source 2 is applied to theworkpieces 16 to be brazed so that a working arc can be struck betweenthe electrode 28 and the workpieces 16.

[0028] However, it is also possible to generate an arc 15 that is nottransmitted—indicated by broken lines—in which case the non-consumableelectrode 28 is connected to the negative potential 34 in particular ofthe current source 2, whereas the plasma nozzle 27 is connected via aswitching device 36 to the other, in particular positive, potential 35of the current source 2.

[0029] In order to give the user the option of selecting a transmittedor a non-transmitted working arc as required, the switching device 36can be switched to different positions enabling the best operating modeto be selected at any time, depending on the material of the workpieces16. Naturally, the system could be set up so that the arc is transmittedonly or not transmitted only or both operations run at the same time.

[0030] In order to run a brazing process to join the workpieces 16 to bejoined using the structure illustrated here, a filler material 38, inthe form of one or more wires, in particular one or more endless weldingwires, schematically indicated as a welding wire, is fed into the seamregion 37 of the workpieces 16 to be joined. In the embodimentillustrated as an example here, the filler material 38 is connected toanother current source 39 and a potential 40 of the current source 39,negative in particular, is applied to the filler material 38 whilst theother, in particular positive, potential 41 is applied to the workpieces16, the current source 39, in particular the power supply of the currentsource 39, being regulated in such a way that when the filler material38 is lifted off the workpiece 16 or moved away from a pool of melt 42,an arc is prevented from being struck.

[0031] As a result of this additional power supply, a current circuit isestablished when the filler material 38 comes into contact with theworkpiece 16 and the resultant flow of current heats the filler material38. To ensure that heating of the filler material 38 is kept constant,the filler material 38 is placed in contact with the workpiece 16 or thepool of melt 42, formed by the liquefied filler material 38 during aprocess, in particular during a brazing process. It would naturally alsobe possible to use only a single current source 2 or 39 instead ofproviding a second current source 39. In situations where only a singlecurrent source 2 or 39 is used, the latter is set up so that it has twopower circuits which can be regulated and controlled separately from oneanother, thereby enabling the arc and the current circuit via the fillermaterial 38 to be supplied with power independently of one another.

[0032] The current source 39 supplies the filler material 38 with power,in particular with a variable, constant or pulsed current, in such a waythat the filler material 38 is heated to just below its meltingtemperature. The settings at the current source 39 may be specificallyadapted to the particular material used for the filler material 38, forexample, enabling the settings to be automatically retrieved from valuesstored accordingly. Clearly, it would also be possible for a user toinput the parameters, in particular the current level, directly at thecurrent source 39. The current source 39 also ensures that if the fillermaterial 38 is undesirably lifted away from the workpiece 16 or is movedaway from the pool of melt 42, an arc, which would cause the basematerial of the workpieces 16 to melt, is prevented.

[0033] As a result of the specific amount of heat introduced into thefiller material 38 and because the filler material 38 is heated, thepower supply of the working arc, in particular a plasma arc power, isreduced to a value at which it is predominantly the base material of theworkpieces 16 which is heated and only a residual amount of energy isdelivered to the filler material 38 to fully melt it, i.e. the power ofthe plasma arc can be reduced to the degree that the resultant plasmaarc or working arc can be guaranteed not to melt the base material ofthe workpieces 16 and the workpieces 16 are now merely heated. It maytherefore be said that the power supply of the working arc, inparticular the plasma arc power, is controlled in such a way that thebase material of the workpieces 16 does not melt at all.

[0034] As a result of the so-called hot wire technique, in other wordsby additionally heating the filler material, the pool of melt reaches asignificantly higher temperature because heat is applied simultaneouslyto the pool of melt 42 by the plasma beam or working arc and to thefiller material 38, which means that not so much heat is absorbed by thefiller material 38 as would be if it had not been not heated, i.e. instandard brazing process known from the prior art, the filler material38 is not heated and is therefore dipped cold into the pool of melt 42,which means that the filler material 38 needs to absorb a high amount ofenergy in order for it to melt and this heat energy is therefore drawnoff from the pool of melt 42 and plasma beam or the working arc. Inorder to be able to compensate for this, it is then necessary toincrease the power level, in particular the plasma arc power, and thereis no longer any guarantee that the base material of the workpieces 16will not melt.

[0035] As a result of the high melt pool temperature which can now beobtained, the wettability of the filler material 38, in particular thewelding wire or braze delivered, is very much increased. The reliabilityof the process is also significantly improved without having to applymore energy to the base material of the workpieces 16. The essentialfactor with the method proposed by the invention is that the fillermaterial 3 8 is pre-heated to the degree that only a small amount ofheat is then needed to render the filler material 38 liquid.Furthermore, because of the high melt pool temperature and because thefiller material 38 is pre-heated, the filler material 38 used may be onewhose melting point is the same as or higher than the base material ofthe workpieces 16, because the filler material 38 is heated separatelyby the current source 39 to just below the melting point of the fillermaterial 38 and the residual energy needed to render the filler material38 liquid is supplied by the plasma beam or working arc.

[0036] Since the operating sequence of the method is the same as thatused in the prior art, it will not be described in detail. It shouldmerely be mentioned that, at the start of brazing, in other words at thestart of the process, the current source 2 for the working arc isswitched on first of all, for example, so that the working arc and hencea hot plasma beam can be generated from the start. The wire feed device11 (not illustrated in FIG. 2) and the current source 39 for the fillermaterial 38 are then switched on so that a current circuit can beestablished when the filler material 38 comes into contact with theworkpiece, thereby enabling a heating phase of the brazing process to berun if necessary, depending on the sequence. The brazing process is runin the same way as a welding process, i.e. the torch 10 is guided alongthe joining point of the two workpieces 16 and a pool of melt 42 isformed from the filler material 38 accordingly.

[0037] During this process, the current source 39 for the fillermaterial 38 may be provided in the form of a constant current sourcewith voltage limitation so that an arc is not formed when the fillermaterial 38 is moved out of the pool of melt 42 or is lifted away fromthe workpiece 16. The current source 39 is therefore operated inconstant current mode or pulsed mode, and if operated in pulsed mode,synchronous wire pulses are also possible, i.e. the filler material isfed along at a constant or pulsed wire feed rate, in other words thefiller material 38 is fed in a forwards/backwards motion or aforwards/stop motion.

[0038]FIG. 3 illustrates another embodiment using a welding torch of atype known form the prior art. Since the basic structure of this type oftorch 10 is known, it will not be described in detail.

[0039] The torch 10, in particular the welding torch, has a contact tube43, through which a consumable welding wire 13 acting as an electrode isfed, the contact tube 43 being enclosed by a gas nozzle 31. In theembodiment illustrated as an example here, the filler material 38, whichis again connected to the current source 39, is fed to the seam region37 and to the workpieces 16 externally to the torch 10, as schematicallyindicated. The filler material 38 may be fed from the wire feed device11 (illustrated in FIG. 1) through a guide device, which may be attachedto the torch 10—not illustrated—for example.

[0040] Since the plasma arc power can be reduced in the manner describedin connection with FIG. 2 as a result of the method proposed by theinvention, a consumable welding wire 13 can now serve or be used as theelectrode, i.e. the plasma arc power, in particular the power supply forthe arc 15 struck between the welding wire 13 and the workpieces 16 isregulated in such a way that melting of the welding wire 13 andsimultaneously melting of the base material of the workpieces 16 isprevented. The base material of the workpieces 16 is now heated by thearc 15 or the plasma arc. It may therefore be said that a consumablewelding wire 13 is used as an electrode and the power supply of thewelding wire 13 is controlled in such a way that the welding wire 13 isprevented from melting and a brazing process can be run by feeding andheating the filler material 38.

[0041] As descried above in connection with FIG. 2, the filler material38 is heated by a separate current circuit, in particular the currentcircuit 39, so that as the filler material 38 is fed along, the low arcpower of the arc 15 or working arc is enough to heat the base materialas necessary and simultaneously make up the heat energy still needed torender the filler material 38 liquid.

[0042] Using a set-up of this type, therefore, it is possible to run awelding process with a welding torch, during which the base material ofthe workpieces 16 is fused and the welding wire 13 melted accordingly,and to run a brazing process during which a filler material 38 is fedalong and melted. All that is needed to achieve this is that the fillermaterial 38 and the welding parameters must be controlled accordingly,i.e. during a welding process, the filler material 38 is swung or fedexternally to the welding area or seam region 37 and the weldingparameters raised in order to melt the welding wire 13, whereas in abrazing process the controls and regulations described in connectionwith FIG. 2 are applied.

[0043] Consequently, using only one torch 10 or only one welding/brazingsystem, such as used on a production line in the automotive industry forexample, two different processes can be run consecutively, namely awelding process and a brazing process, without the need for two separatesets of apparatus, as is currently the case, i.e. in the case of bodybuilding, for example, all the brazed joints can be made first with thewelding torch 10 and then afterwards the weld joints, or vice versa, onthe same vehicle body with the same torch 10 or with the samewelding/brazing apparatus. The only thing needed to achieve this is toprogramme or set the individual parameters to run the processaccordingly.

[0044] Naturally, if using a two-wire or multi-wire torch 10 where eachof the individually fed welding wires 13 has a separate current circuit,, these may be controlled or regulated in such a way that one weldingwire 13 acts as the electrode and the arc is controlled so that nomelting occurs and the or the other welding wires 13 is/are operated asthe filler material 38 and are heated via the current circuit.Consequently, one welding wire 13 can be replaced by a non-consumableelectrode. A torch 10 can therefore be used in which all the wiresdelivered, in particular the welding wires 13 or filler materials 38,are disposed inside the torch 10. A torch 10 of this type could thenalso be used to run a welding process and a brazing process in turn bysetting the welding parameters accordingly, as described above.

[0045] For the sake of good order, it should be pointed out that inorder to provide a clearer understanding of the structure of the weldingdevice 1, it and its constituent parts are illustrated to a certainextent out of proportion and/or on an enlarged and/or reduced scale.

[0046] The individual solutions used by the invention to achieve the setobjective may be found in the description.

[0047] Above all, the individual embodiments illustrated in FIGS. 1; 2;3 may be construed as independent solutions proposed by the invention intheir own right. The associated objectives and solutions proposed by theinvention may be found in the detailed description of the drawings.

List of Reference Numbers

[0048]1 Welding device

[0049]2 Current source

[0050]3 Power component

[0051]4 Control system

[0052]5 Switching element

[0053]6 Control valve

[0054]7 Supply line

[0055]8 Gas

[0056]9 Gas storage

[0057]10 Torch

[0058]11 Wire feed device

[0059]12 Supply line

[0060]13 Welding wire

[0061]14 Supply reel

[0062]15 Arc

[0063]16 Workpiece

[0064]17 Welding line

[0065]18 Welding line

[0066]19 Coolant circuit

[0067]20 Flow indicator

[0068]21 Water container

[0069]22 Input and/or output device

[0070]23 Hose pack

[0071]24 Connecting device

[0072]25 Tension-relieving device

[0073]26 Housing

[0074]27 Plasma nozzle

[0075]28 Electrode

[0076]29 Passage

[0077]30 Arrow

[0078]31 Gas nozzle

[0079]32 Passage

[0080]33 Arrow

[0081]34 Potential

[0082]35 Potential

[0083]36 Switching device

[0084]37 Seam region

[0085]38 Filler material

[0086]39 Seam region

[0087]40 Potential

[0088]41 Potential

[0089]42 Poll of melt

[0090]43 Contact tube

1. Method of brazing workpieces with a torch, in particular a plasma orwelding torch, having an electrode, in which a transmitted and/ornon-transmitted working arc, supplied with power from a power source ora current source, is produced in order to generate a plasma beam from adelivered plasma gas, whereby at least one filler material is fed to theseam region of the workpieces to be joined, characterised in that thefiller material (38) is connected to the or to another power source orcurrent source (2, 3 9) and to this end one potential (34, 35, 40, 41)of the power source or current source (2, 39) is applied to the fillermaterial (38) and the other potential (34, 35, 40, 41) to the workpieces(16), and the power source or current source (2, 39), in particular thepower delivered by the power source or current source (2, 39), isregulated in such a way that when the filler material (38) is lifted offthe workpiece (16) an arc is prevented from being struck.
 2. Method asclaimed in claim 1, characterised in that the filler material (38) isplaced in contact with the workpiece (16) or a pool of melt (42) duringthe brazing process.
 3. Method as claimed in claim 1 or 2, characterisedin that if a single current source (2 or 39) is used, it is set up so asto have two power circuits which can be controlled and regulatedseparately from one another.
 4. Method as claimed in one or more of thepreceding claims, characterised in that the filler material (38) issupplied with power, in particular with a variable, constant or pulsedcurrent, in such a way that the filler material (38) is heated to justbelow its melting temperature.
 5. Method as claimed in one or more ofthe preceding claims, characterised in that by applying a specificamount of heat to the filler material (38), the power supply of theworking arc, in particular the plasma arc power, can be reduced to avalue at which it is predominantly the base material of the workpieces(16) which is heated and only a residual amount of energy needed tofully melt it is applied to the filler material (3).
 6. Method asclaimed in one or more of the preceding claims, characterised in thatthe power supply of the working arc, in particular the plasma arc power,is regulated in such a way that the base material of the workpieces (16)does not melt.
 7. Method as claimed in one or more of the precedingclaims, characterised in that the filler material (38) is fed in theform of one or more wires, in particular one or more endless weldingwires (13).
 8. Method as claimed in one or more of the preceding claims,characterised in that the filler material (38) is fed at a constant orpulsed wire feed rate.
 9. Method as claimed in one or more of thepreceding claims, characterised in that the melting point of the fillermaterial (38) is the same as or higher than the base material of theworkpieces (16).
 10. Method as claimed in one or more of the precedingclaims, characterised in that a consumable welding wire (13) is used asan electrode and the power supply of the welding wire (13) is regulatedin such a way that the welding wire (13) is prevented from melting. 11.Plasma or welding device for brazing workpieces with a torch, inparticular a plasma or welding torch, having an electrode, in which thetorch is connected to a current source in order to produce a transmittedor a non-transmitted working arc to generate a plasma beam from adelivered plasma gas, and at least one filler material is fed to theseam region of the workpieces to be joined, characterised in that thefiller material (38) is connected to the or to another current source(2, 39) and one potential (34, 35, 40, 41) of the current source (2, 39)is applied to the filler material (38) and the other potential (34, 35,40, 41) to the workpieces (16).
 12. Plasma or welding device as claimedin claim 11, characterised in that the current source (2, 39), inparticular the power supply of the current source (2, 39), is controlledand regulated in such a way that when the filler material (38) is liftedoff the workpiece (16) no arc is generated.